TANTALUM 311 



Intake Levels. Tantalum is not of importance in regard to its natural 

 occurrence in biological materials. The LD50 for tantalum chloride in 

 rats was 958 mg/kg of the metal for ingestion and 38 for intraperitoneal 

 administration. Tantalum oxide, which is highly insoluble, was con- 

 sidered nontoxic, since oral doses of 8 g/kg produced no symptoms in 

 rats (Ta-1). Tantalum has been used as a source of gamma radiation. 



Radioassay. Gamma counting is preferred when possible, since self- 

 absorption corrections are thus eliminated and tissues can be measured 

 directly. 



Chemistry. Conventional wet- or dry-ashing is satisfactory. Meth- 

 ods for chemical estimation of tantalum in biological materials are not 

 available. 



Typical Methods. Sheep were given orally about 5 mc Ta"^- as potas- 

 sium tantalate. Tissue samples were dry-ashed at about 550°C', and the 

 ash spread uniformly on porcelain dishes for counting with a thin-mica- 

 window counter (Ta-2). 



Ta-1. Cochran, Kenneth W., John Doull, Marcella Mazur, and Kenneth P. DuBois: 

 Acute Toxicity of Zirconium, Columbium, Strontium, Lanthanum, Cesium, 

 Tantalum and Yttrium, Arch. Ind. Hyg. and Occupational Med., 1: 037-650 

 (1950). 



Ta-2. Comar, C. L., and I. B. Whitney: Unpul^lished results. 



